Both elevator and escalator systems include a plurality of safety devices which are monitored to ensure proper operation. Typically, these devices are used to provide shutdown of the escalator or elevator when an undesirable condition exists. A typical such system includes a plurality of series connected contacts so that if one contact opens, the safety circuit opens. The safety circuit is commonly referred to as a "safety string".
A difficulty with a typical safety string circuit exists when trouble shooting is required. When a contact in the string opens, it is not readily apparent which contact has opened. The typical elevator or escalator system may include twenty or more contacts in the safety string. Desirably, troubleshooting can be done from a central location.
A device known as a "smart switch" has been developed. A smart switch typically includes a switch connected to a microcontroller. The microcontroller can be connected to a main controller using a serial link. In an elevator or escalator system, a smart switch can be used for each of the devices in the safety string, with the microcontroller of each device providing status information to the main controller. With the use of smart switches, the hard wired safety string circuit remains with the microcontroller of each providing switch status information to the main controller so that the main controller can identify which device in the string has sensed an error condition.
A further problem remains in that the smart switch could fail with its contact in a closed condition, so that any further error would not be sensed. Desirably, the main controller should be able to detect the operability of the safety switches in the elevator or escalator system.
Similarly, with elevator systems the main controller responds to service commands issued at call stations located remotely from the main controller. These call stations may also use smart switches connected to the main controller for which operability should be determined.
The present invention is directed to solving one or more of the problems discussed above in a novel and simple manner.